The linear motion guiding device that includes the ball as the rolling element includes a guide rail, a slider, and a plurality of balls. The slider is provided at an outside of the guide rail. The guide rail and the slider face with each other and respectively have, at facing positions, raceway grooves that form raceways of the balls. Both of the raceway grooves extend in a longer direction of the guide rail.
The slider includes a slider main body and a pair of end caps, the raceway groove and a return path of the ball are formed to the slider main body, and the direction changing passage of the ball is formed to the end cap. The ball is provided in the circulation pathway including the raceway, the return path, and the direction changing passage, and via the ball that rolls within the raceway in a load state, the slider linearly moves along the guide rail.
Formed on a surface of a side of the slider main body of the end cap, is a groove that forms the outer peripheral surface of the direction changing passage and includes an arc-shaped cross section (hereinafter, referred to as “arc groove”). Formed on an end of a side of the raceway of the arc groove is a tongue unit that scoops up the ball from the raceway and guides the ball to the direction changing passage.
When the linear motion guiding device is driven at a high speed, since the ball repeatedly clashes with the tongue unit of the end cap at high speed, a damage easily occurs to the tongue unit. Therefore, conventionally, a method for enhancing the stiffness of the tongue unit has been proposed.
For example, PTL 1 proposes to make a tip, to which the ball clashes, of the tongue unit to be a planar tip that is perpendicular to the direction in which the raceway (rolling element rolling passages) extends, a convex tip, or concave tip having a curvature radius of the radius or more of the ball. Accordingly, compared to a case when the tip is sharp, the contact area after the elastic deformation associated with the clash of the ball becomes large (when tip is concave, surface contact may occur), and thus, PTL 1 discloses that the contact pressure becomes small and the plastic deformation (damage) is unlikely to occur to the tip.
PTL 2 proposes that a portion of a front of at least the tongue unit of the arc groove is made to form Gothic arc shape, and by rendering the ball in a two-point contact state at the front of the tongue unit, the impact force applied to the ball is dispersed.
PTL 2 further discloses that when a line connecting the contact point of the ball relative to the tongue unit (scooping unit) with the center of the ball contacted with the tongue unit is L10, and a line connecting the center of the ball contacted with the tongue unit and the groove bottom of the Gothic arc shaped arc groove is L20, an angle between L10 and L20 is preferably 40 degrees or more and 60 degrees or less.
PTL 3 discloses that only the tongue unit (rolling element scoop-up unit that scoops up rolling element from load rolling path to direction changing passage) is separated from the end cap, the end cap includes a main body and the tongue unit attached thereto, and the tongue unit is formed by a material having higher shock resistance than that of the main body. The tongue unit is, via a fastening member such as thread, fixed to the main body.